For many applications, for example in optical pre-amplifiers, it is desirable to operate an optical amplifier in a mode of operation such that either the output optical power of the amplifier or the gain of the optical amplifier is maintained at a constant level. These modes of operation are referred to as constant output power mode and constant gain mode respectively.
The total optical output power of an amplifier consists of both amplified signal power and amplified spontaneous emission (ASE) power. Existing amplifiers rely on automatic power control (APC) to maintain the total optical power of the amplifier at a constant level. Therefore, existing APC implementations are unable to determine the usable optical signal power and optical network engineers are forced to allow additional margins in their optical power-budget design or operate the amplifier in automatic gain control (AGC) where an ASE correction is easier to implement.